Telomeres are specialized structures on chromosome ends that are essential for genome stability and cellular replicative capacity. Maintenance of proper telomere structure and length allows continued cell division. However, most replicating cells in the body do not express the maintenance enzyme telomerase and gradually lose telomeric DNA, eventually reaching a critically short telomere length that triggers cellular senescence and/or apoptosis. Theoretically, significant accumulation of senescent cells or loss of apoptotic cells in tissues occurs late in life and may underlie development of certain normal aging characteristics. However, solid support for the relationship between telomere dysfunction, cellular senescence and possible aging phenotypes in normal individuals is currently lacking. The premature aging disease Werner syndrome (WS) that shows early onset and increased frequency of many deleterious aging features (including cancer, atherosclerosis, osteoporosis, cataracts, diabetes, and hypertension) is caused by loss of function of a single protein, WRN. Cells derived from WS patients show telomeric abnormalities and a dramatic premature cellular senescence that is prevented by prior expression of telomerase. Investigations from several laboratories (including ours) indicate that WRN functions in telomere maintenance, possibly in coordination with the telomeric protein TRF2. Thus, WS is an excellent model for studying the relationships between telomere maintenance, cellular senescence, apoptosis, and development of specific aging characteristics. This proposal will examine the biochemical activities of WRN (in conjunction with TRF2 and other telomeric factors) on relevant telomeric DNA structures and determine its protein partners during its function in telomere metabolism with specific emphasis on telomeric replication. In addition, telomere dynamics (replication kinetics and length alterations) and cellular senescence in normal and WS cells will be examined during chronic treatment with selected DNA damaging agents. These studies will clarify the telomeric function of WRN and determine whether persistent DNA lesions in telomeric regions exacerbate telomere loss over time in WS cells compared to normal cells, and provide further support to the role of telomere dysfunction in the development of specific age-related characteristics in WS as well as in normal aging. Thus, this proposal will implicate and examine basic mechanisms at work in genome maintenance and suppression of certain aging phenotypes as well as cancer. PUBLIC HEALTH RELEVANCE: This proposal examines the role of a specific protein, WRN, in the maintenance of chromosome ends, otherwise known as telomeres. When the function of human WRN is lost (in the hereditary disease Werner syndrome), the resulting telomeric abnormalities trigger cell senescence or cell death and, in time, cause early development of aging features and cancer in affected individuals. By investigating Werner syndrome and the role of WRN in telomere metabolism, this proposal will help understand basic cellular mechanisms that act to suppress development of specific aging characteristics as well as cancer.